Abstract P3-01-09: Re-evaluating the “10% rule” for sentinel lymph node biopsy with radioactive method in breast cancer; a single institutional retrospective study

Background: When multiple radioactive sentinel lymph nodes (SLNs) are present during sentinel lymph node biopsy (SLNB), excision of those SLNs with >10% radioactive count per minute (high-CPM) of the most radioactive node (“10% rule”) has been proposed. Although this “10% rule” may avoid excessive removal of SLNs,the risk of false negative and remnant positive SLNs in the patients who have SLNs with Method: We reviewed the records of successful SLNBs using the radioisotope (RI) method performed between January 2001 and December 2016 in our institution. The radioactive count from each excised SLN was measured. Non-radioactive lymph nodes were excluded from this analysis. All SLNs were pathologically assessed by 2mm serial section with hematoxylin and eosin staining. Results: In the 3,043 patients with successful SLNB,the median number of radioactive SLNs removed was 2 (mean, 1.8; range, 1-10) and 599 patients (19.7%) had SLNs with low-CPM. The total number of radioactive SLNs was 5,472, and 875 (16.0%) out of 5,472 SLNs were low-CPM. Sixty-one (7.0%) out of these 875 SLNs with low CPM in 56 patients (1.8%) had metastatic disease by pathological assessment. The number of metastatic SLN with low-CPM was one in 51 patients and two in 5 patients. Nineteen patients (0.6%) had no metastatic lesion in SLNs with high-CPM. Discussion and Conclusions: If SLNB was performed by RI method alone with “10% rule”, false negative rate increased by 0.6% and underestimation increased up to 1.8%. Furthermore, 19.7% of the patients have the benefit of avoiding excessive removal of SLNs.Considering the risk and benefit, “10% rule” is a high validitymethod to capture metastatic SLNs even in the setting that ALND will not be performed. Citation Format: Miyamoto H, Aruga T, Onishi M, Goto R, Iwamoto N, Idera N, Horiguchi K, Honda Y. Re-evaluating the “10% rule” for sentinel lymph node biopsy with radioactive method in breast cancer; a single institutional retrospective study [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-01-09.